Previous studies showed that food has a profound effect on the enteral absorption of chlorothiazide, but not that of hydrochlorothiazide. Specific interactions between cephradine and peptides are equivocal. Proposed studies will concentrate on 6 major areas: (1) The bioavailability of hydroflumethiazide will be challenged under various conditions. Information will thus be obtained on three common diuretics. Observed absorption characteristics will be interpreted mechanistically with respect to drug physical/chemical characteristics. (2) The bioavailability study for hydrocortisone has started. There is little information on this compound, although its pharmacokinetic characteristics are known to be affected by drug concentration-dependent binding to transcortin and serum albumin. (3) Studies on cephalosporin bioavailability are planned. The emphasis will be both clinical and mechanistic. The influence of food on the relative oral availability of cephradine, cephalexin, and cefactor will be examined. This will include direct challenge of cephalosporin absorption by protein hydrolysate. (4) The bioavailability of oral levodopa will be examined in the presence of protein. (5) Specific relationships between alcohol volume and absorption characteristics with particular reference to stomach emptying, and saturable absorption will be examined. (6) Consideration will be given to interactions influencing theophylline or acetazolamide absorption from sustained or delayed release formulations.